4.Angular deviation correction

*Earth Crust*

3.Coarse error elimination

be deleted.

Set a reasonable threshold for the side-scan data energy. If the energy of side-scan data is lower than the threshold, it indicates a bad ping and should

**42**

**Figure 12.**

*Flow diagram of data processing and mapping.*

Analyze existing BSSS data and select data corresponding to the seafloor with a constant slope. Let the slope pass the point just below the sonar array to find the optimal slope of the seafloor; use this slope to obtain the angle correction curve of bathymetric data. Next, use median filter to filter the obtained angle correction curve, filter out high-frequency components, and retain only lowfrequency components to reflect the larger change trend. Finally, use the angle correction curve to perform angle correction on each ping data.

5.Port/starboard position correction

Read ping data in the BSSS data file, obtain the delay and angle of each ping, and convert to slant range and angle. Calculate the horizontal distance and the vertical height of each ping according to the triangular geometric relationship (taking the installation angle of the sonar array into consideration). Add the port/starboard position to the horizontal distance while maintaining the vertical height. Recalculate the corresponding slant range and angle according to the triangular geometric relationship and convert to delay and angle.

## **5.2 Data post-processing**

1.Installation angle correction

Correct the installation angle with 30°, which is measured.

2.Sound velocity correction

Input the measured sound velocity by CTD.

3.Attitude data filtering

Perform median filtering and smoothing for roll, pitch, and heading.

4.Bathymetric data filtering

Filter bathymetric data by setting the height, horizontal coordinates, depth, and slant distance.

5.Fine error elimination

Trim the pings manually to realize fine error elimination.

6.Field correction

If there is a suitable swath, select the swath that meets the requirements, carry out the corresponding error test, and make corresponding corrections to suppress deviation of the roll, navigation latency, and pitch.

7.Side-scan data filtering

Filter side-scan data by setting the height, horizontal coordinates, depth, and slant distance.

8.Bottom tracking

Side-scan data processing requires bottom tracking to delete the water column and generally selects automatic bottom tracking. If the effect is not appropriate, bottom tracking can be manually set.

9.Angle variation gain

Angle variation gain is used to compensate for backscattering variations due to system beam pattern irregularities and incident angle changes.

10.Gain equalization

Gain equalization can be used to address the unevenness of side-scan data due to hardware gain changes or excessive pitch angles during data acquisition.

11.Data export

Export processed data for mapping.

12.Mapping

Use Surfer software to perform topographical and geomorphological mapping.
